Process for removing organic substances and nitrogen compounds from waste water

Abstract

An improved process for the removal of organic substances and nitrogen compounds from waste water by means of micro-organisms, wherein waste water to be treated is passed continuously through a denitrification zone, effluent from the denitrification zone is passed into a nitrification zone, and at least a portion of the effluent from the nitrification zone is recycled back to the denitrification zone. A portion of the waste water to be treated is fed directly into the nitrification zone as well as to the denitrification zone.

We claim: 
     
       1. In a process for the removal of organic substances and nitrogen compounds from waste water by means of micro-organisms wherein: waste water to be treated is passed continuously through a denitrification zone;   effluent from said denitrification zone is passed through a nitrification zone; and   at least a portion of the effluent from the nitrification zone is recycled to the denitrification zone and the remaining portion is discharged, the improvement wherein a portion of said waste water to be treated is fed directly to said nitrification zone.     
     
     
       2. The process of claim 1 wherein the ratio of the amount of waste water flow passed into the denitrification zone to the amount of the waste water flow passed directly to the nitrification zone, as well as the amount of effluent from the nitrification zone recycled to the denitrification zone, are so controlled that the effluent from the denitrification zone contains nitrate. 
     
     
       3. The process of claim 2 wherein the nitrate content of the effluent from the denitrification zone is at least 0.5 mg per liter. 
     
     
       4. The process of claim 1 or 2 wherein at least 25% of the effluent from the nitrification zone is returned to the denitrification zone. 
     
     
       5. The process of claim 1 wherein the denitrification is effected in at least one rising-flow reactor. 
     
     
       6. The process of claim 5 wherein the denitrification is effected in at least two series-connected rising-flow reactors. 
     
     
       7. The process of claim 5 wherein pH of the liquid in said at least one rising-flow reactor is controlled at 8.0 or higher. 
     
     
       8. The process of claim 1 or 5 wherein said remaining portion of nitrification zone effluent is discharged into further processing steps wherein it is substantially freed of sludge and thereafter treated in an alternately aerated and non-aerated reactor to which a further portion of said waste water to be treated is fed. 
     
     
       9. The process of claim 1 or 5 wherein the nitrification zone is alternately aerated and non-aerated. 
     
     
       10. The process of claim 9 wherein the nitrification zone consists of two nitrification reactors connected in parallel, and each such reactor is alternately aerated and non-aerated in a manner such that one is aerated while the other is not. 
     
     
       11. The process of claim 10 wherein said portion of waste water to be treated is fed directly to the reactor not being aerated. 
     
     
       12. The process of claim 1 or 5 wherein said remaining portion of nitrification zone effluent is subjected to an additional aeration step after which it is substantially freed of sludge.